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I have an app that I want to parse using JSON, it outputs data in the following format for each frame of a video...

root@nvidia-desktop:/home/nvidia# cat test.json 
{"version":2,"data_type":"alpr_results","epoch_time":1567039688133,"img_width":1920,"img_height":1080,"processing_time_ms":133.36436462402344,"uuid":"","error":false,"regions_of_interest":[{"x":0,"y":0,"width":1920,"height":1080}],"results":[{"plate":"LRK290","confidence":77.8797607421875,"matches_template":0,"plate_index":0,"region":"nz-auk","region_confidence":57,"processing_time_ms":73.737274169921875,"requested_topn":10,"coordinates":[{"x":667,"y":435},{"x":718,"y":433},{"x":718,"y":447},{"x":668,"y":449}],"vehicle_region":{"x":614,"y":336,"width":158,"height":158},"candidates":[{"plate":"LRK290","confidence":77.8797607421875,"matches_template":0},{"plate":"CRK290","confidence":71.4766616821289,"matches_template":0},{"plate":"RK290","confidence":69.619705200195312,"matches_template":0},{"plate":"ERK290","confidence":67.774589538574219,"matches_template":0},{"plate":"NRK290","confidence":67.747268676757812,"matches_template":0},{"plate":"QRK290","confidence":67.733123779296875,"matches_template":0},{"plate":"MRK290","confidence":67.732582092285156,"matches_template":0},{"plate":"ARK290","confidence":67.731903076171875,"matches_template":0},{"plate":"URK290","confidence":67.73187255859375,"matches_template":0},{"plate":"HRK290","confidence":67.7306137084961,"matches_template":0}]}]}
{"version":2,"data_type":"alpr_results","epoch_time":1567039688133,"img_width":1920,"img_height":1080,"processing_time_ms":133.36436462402344,"uuid":"","error":false,"regions_of_interest":[{"x":0,"y":0,"width":1920,"height":1080}],"results":[{"plate":"LRK298","confidence":73.848838806152344,"matches_template":0,"plate_index":0,"region":"nz-auk","region_confidence":60,"processing_time_ms":73.737274169921875,"requested_topn":10,"coordinates":[{"x":674,"y":439},{"x":724,"y":440},{"x":725,"y":457},{"x":675,"y":457}],"vehicle_region":{"x":600,"y":315,"width":199,"height":199},"candidates":[{"plate":"LRK298","confidence":73.848838806152344,"matches_template":0},{"plate":"LRK290","confidence":70.1683120727539,"matches_template":0},{"plate":"LRK29","confidence":65.916587829589844,"matches_template":0},{"plate":"LRK292","confidence":65.307365417480469,"matches_template":0},{"plate":"LRK293","confidence":65.293647766113281,"matches_template":0},{"plate":"LRK299","confidence":65.292098999023438,"matches_template":0},{"plate":"LRK29Q","confidence":65.289726257324219,"matches_template":0},{"plate":"LR298","confidence":61.362815856933594,"matches_template":0},{"plate":"RK298","confidence":60.530429840087891,"matches_template":0},{"plate":"LK298","confidence":60.528419494628906,"matches_template":0}]}]}
{"version":2,"data_type":"alpr_results","epoch_time":1567039688133,"img_width":1920,"img_height":1080,"processing_time_ms":133.36436462402344,"uuid":"","error":false,"regions_of_interest":[{"x":0,"y":0,"width":1920,"height":1080}],"results":[{"plate":"LRK298","confidence":82.452705383300781,"matches_template":0,"plate_index":0,"region":"nz-can","region_confidence":34,"processing_time_ms":73.737274169921875,"requested_topn":10,"coordinates":[{"x":687,"y":444},{"x":735,"y":443},{"x":737,"y":462},{"x":688,"y":463}],"vehicle_region":{"x":604,"y":310,"width":215,"height":215},"candidates":[{"plate":"LRK298","confidence":82.452705383300781,"matches_template":0},{"plate":"LRK290","confidence":73.113128662109375,"matches_template":0},{"plate":"LRK29","confidence":70.9032211303711,"matches_template":0},{"plate":"LRK292","confidence":70.755508422851562,"matches_template":0},{"plate":"LRK293","confidence":70.6309814453125,"matches_template":0},{"plate":"LRK299","confidence":70.598648071289062,"matches_template":0},{"plate":"RK298","confidence":69.2212905883789,"matches_template":0},{"plate":"LR298","confidence":68.384689331054688,"matches_template":0},{"plate":"CRK298","confidence":68.189926147460938,"matches_template":0},{"plate":"NRK298","confidence":68.101593017578125,"matches_template":0}]}]}

Here is is working with a single entry in test.json

root@nvidia-desktop:/home/nvidia# cat test.json | python -c 'import json,sys;obj=json.load(sys.stdin);print obj["results"][0]["plate"]'
LRK290
root@nvidia-desktop:/home/nvidia#

But it fails with multiple entries (which is what I'm wanting)

root@nvidia-desktop:/home/nvidia# cat test.json | python -c 'import json,sys;obj=json.load(sys.stdin);print obj["results"][0]["plate"]'
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/usr/lib/python2.7/json/__init__.py", line 291, in load
    **kw)
  File "/usr/lib/python2.7/json/__init__.py", line 339, in loads
    return _default_decoder.decode(s)
  File "/usr/lib/python2.7/json/decoder.py", line 367, in decode
    raise ValueError(errmsg("Extra data", s, end, len(s)))
ValueError: Extra data: line 2 column 1 - line 5 column 1 (char 1306 - 3924)
root@nvidia-desktop:/home/nvidia#
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1 Answer 1

Reset to default
3

Try reading stdin one line at a time, e.g.:

$ python -c 'import json,sys
for line in sys.stdin:
  obj=json.loads(line)
  print obj["results"][0]["plate"]' < test.json 
LRK290
LRK298
LRK298

If python isn't a hard requirement, jq works too:

$ jq -r .results[0].plate test.json  
LRK290
LRK298
LRK298

The -r option gives raw output. Without -r, you'll get JSON encoded output (double-quoted strings in this case).

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